Measurement devices which are used for example in the field of monitoring objects or monitoring bulk material emit electromagnetic waves or ultrasound waves in the form of a transmission signal, for example, which are reflected at least in part from the filling material surface or the corresponding object. The transmission signal (also referred to as the “measurement signal”) which is reflected at least in part can then be received by the antenna unit of the measurement device and analysed by the electronics connected thereto.
By scanning over the surface of the filling material or object, it is possible to determine the topology of the filling material surface or the object, respectively. In the field of fill level measurement, “topology” is understood to mean the shape of the surface of the filling material or bulk material. In this context, the term “topography” can also be used.
In order to supply the measurement devices with electrical power and transmit the obtained data to an external device, the measurement devices can be equipped with what is referred to as a “four-wire interface”. In an alternative configuration, such measurement devices can also be equipped with what is referred to as a “two-wire interface” (4-20 mA interface).
In order to detect the topology of the filling material surface, it is possible to make the entire fill level measurement device (for example a radar level indicator) rotate. It is also possible to make just the transmitting and/or receiving unit, referred to in the following as the “antenna unit”, rotate. In this case, the transmission signal can be transmitted from the high-frequency unit, located in the housing of the fill level measurement device, to the antenna unit by means of a waveguide.